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Tim Allen’S Extreme ImpalaIf Chevrolet had gone into production with an LT5-equipped Impala SS, it would have been the ultimate 160-mph-plus American family dream sedan. Apparently not lacking dough, industry contacts, or imagination, comedian Tim Allen, with the expert help of Chevrolet Motor Division and its chief toy builder Jon Moss, is about to make that particular dream come true, and then some.

Like the Detroit-dwelling character he plays on the hit television series “Home Improvement,” Allen isn’t satisfied with the “standard” engine in any machine. So, his new ride’s special high-compression DOHC 32-valve LT5 from the Corvette ZR-1 has been punched out from 5.7 to 6.3 liters. And power surges upward from a merely sufficient 405 horsepower to a more manly 454 ponies.

Modifications to the Impala’s interior include upgraded leather seats, a faux carbon-fiber trim treatment, a small liquor cabinet and a case for crystal in the rear-seat armrest, pull-out trays in the front-seat backrests, and a redesigned center console with built-in ice bucket, integral cellular phone, and extra power jacks for a laptop computer.

Not surprisingly, slipping the LT5 into this one-off Impala and bolting it to a four-speed automatic was a serious project requiring reprogrammed powertrain software, a custom-designed stainless exhaust system with catalysts, a special heavy-duty aluminum driveshaft, a beefed-up ring-and-pinion set, and a host of other go-faster goodies, including cross-drilled four-wheel discs. When the car is completed and makes it out to its permanent California home, we’ve been promised a ride. If we can latch our test gear onto the beast, we’ll report back.

Can you say, “Binford LT5 6300 series?” -Jack Keebler

The 32-Valve Stampede BeginsWhen Ford finally euthanized the 5.0-liter OHV V-8 in the Mustang, it threw the world of Mustang tuners into a tizzy. Some of the lesser players have folded up shop and slunk on to their next adventure in capitalist subterfuge. Others have resigned themselves to the overhead-cam reality and have made do. A precious few have embraced the new Ford world order enthusiastically and now are producing fascinating variations on the latest from Dearborn.

Among that last group is Kenny Brown Performance, which has introduced its version of the DOHC 32-valve Mustang Cobra. Called the C-4, the package includes 3.73:1 or 4.10:1 gearing in a high-bias differential, cat-back exhaust system, revised suspension, chassis reinforcement, close-ratio shifter, oversize wheels, Bridgestone Expedia S-O4 255/45ZR17 front and 285/40ZR17 rear tires, and all the badges and graphics your wallet can stand. The price is $7950 for the C-4 stuff, which, when applied to a $26,670 Cobra coupe, works out to a $34,620 total tab. And, of course, more options can always be added….

Performance TestFactory-Modified Lexus GS 300Lexus has a strong and lucrative reputation for refined luxury cars. Distinct from their European competitors, Lexus sedans have eschewed the performance edge that lures enthusiast drivers. Nonetheless, the company can produce a sporting sedan; it recently put together a mildly modified GS 300 to showcase the aftermarket possibilities already available. Not only is the car drop-dead gorgeous, it now has the handling confidence to plaster that Starbuck’s Frappuccino to the side of your custom commuter mug.

Complementing the GS 300’s Giugiaro-drawn lines are 18-inch O.Z. Monte Carlo wheels wearing aggressive 235/40ZR18 front and 265/35ZR18 rear Dunlop SP8000s. This wheel and tire combo may seem extreme, but the GS 300 is offered in Europe with 18-inch wheels as a factory option. H&R shocks with coil-over springs lower the front and rear end by 1.0 and 1.5 inches, respectively, to exploit the massive rubber and provide the Lexus an athletic countenance.

The resulting handling limits are daunting; this big-shoed frill machine recorded a Corvette-mimicking 0.91g around the skidpad and stormed through the slalom at 65.4 mph. While the stock GS 300, despite its soft springs and modest tires, already was no slouch in these events (0.82 g and 63.5 mph, respectively), the improvement is commendable.

Of course, some ride quality is sacrificed, but the driving experience retains most of Lexus’ fabled comfort. The big tires also tram disconcertingly along pavement rain grooves, and you must take care when driving over speed bumps or approaching steep driveways to avoid scraping off the car’s underside.

Despite a Brembo braking system with huge 13.1-inch front discs, the 60-0-mph distance was the same as the last stock GS we tested (a ’94): 119 feet. That test misses the point of such big binders, whose real talent is fade resistance after repeated brutal decelerations. Under those conditions, the Brembos are very impressive. Lexus also explained that the ABS computer (which is retained) isn’t designed for such an aggressive brake/tire combination and the wheels may lock up sooner, requiring more ABS cycles to stop the car.

Modifications to the powertrain are limited to a K&N air filter, Borla stainless steel low-restriction mufflers, and porting and polishing the intake manifold and cylinder head using the Extrude Hone process. Together these slight tweaks yield a few more horsepower than the stock 220 at the rear wheels, and it sure sounds good. (Much of the improved acceleration between this GS 300 and the ’94 is also due to the adoption of a five-speed automatic transmission.) The trademark Lexus whisper has been swapped for a sweet, throaty, unobtrusive growl, and the improved breathing allows a bit more lunge as you pull toward the redline.

All these modifications only hint at the potential of the GS 300. In Japan, where this car is sold as the Toyota Aristo, it’s available with all-wheel drive and the twin sequential turbochargers of the Supra Turbo lashed to the big inline-six. As tantalizing as this GS 300 is, let’s hope Lexus brings over the thoroughbred it keeps in the home-market barn. -Scott Goldenberg

Stock

Modified

’94 Lexus

’96 Lexus

GS 300

GS 300

Acceleration

0-60 mph

9.4

8.2

Quarter mile,

sec/mph

16.8/84.4

16.2/86.0

Braking,

60-0, ft

119

119

Slalom,

600-ft, mph

63.5

65.4

Skidpad,

200-ft, lat. g

0.82

0.91

Project AdviceJon Moss’ Secret LT1 Engine Tricks RevealedAbout the closest thing to an official factory hot rodder is Jon Moss, whose innocuous-sounding title is manager of Chevrolet/Geo Specialty Vehicles. That means he’s the guy in charge of putting together Chevy‘s production-based performance and concept vehicles. While Mr. Moss was in Phoenix showing us some of his projects (MT, Aug. ’96), he took time to explain some of the simple tricks and techniques he’s learned for getting the most out of the familiar LT1 small-block V-8 engine, the powerplant found in recent Camaros, Corvettes, Impala SS, and Firebird models. Also enrolled in the conversation was Jeff Beitzel, president of Wheel to Wheel, Inc., Moss’ primary contractor on many of his adventures.

“Induction and exhaust,” explained Moss, “you’ve got to do both, or it’s not worth doing either.” For some LT1-powered vehicles, such as ’93-95 Camaros and Firebirds, cleaning up airflow upstream of the air filter and a simple change in the exhaust system can be worth 11 or 12 horsepower. “There’s a restriction in the exhaust downpipe on the ’93-95 Camaro. A 2.5-inch mandrel-bent pipe in its place makes all the difference in the world. It’s that change in pipe design that was greatly responsible for the increase from 275 to 285 horsepower between the ’95 and ’96 versions of the car.”

With the right induction system, Moss asserts, the ’96 car is capable of 305 horsepower (as in SLP’s Camaro Z28 SS), while a 2.75- or 3.00-inch throughpipe muffler will boost that to 315.

Beyond simple bolt-on induction and exhaust modifications, the most profitable enhancement, according to Moss, is achieved simply by cleaning up the cylinder heads. “Even a good backyard porting job will boost power significantly. Mill the head and you’ll pick up one-half to three-quarters of a point of compression. That will push output up to about 336 horsepower.” Raising the compression ratio will necessitate a move to premium fuels (92 octane or better), as the 10.4:1 ratio of the stock engine is about the maximum that can be tolerated with regular-grade octane ratings.

These sort of simple “blueprinting” operations were used on such vehicles as the Brickyard 400 Camaro Z28 pace car and the six-speed-manual-equipped Impala SS to boost power simply without affecting such untouchable elements as the emissions-control systems. They also parallel some of the changes made by Chevrolet to transform the LT1 into the ’96 Corvette Grand Sport’s 330-horsepower LT4. “Gear changes are significant for the Camaro, too,” continued Beitzel. “The car comes with a 3.42:1 [final drive] ratio with the six-speed, and it can easily handle a 3.73 or 3.92.”

Having driven vehicles modified just as described by Moss and Beitzel, we can attest to the resulting marked, worthy improvements.